1. Field of the Invention
The present invention relates to apparatus for controlling communications, and more specifically to such apparatus to be included in a communication node forming a telecommunications network. The invention also relates to a method of controlling communications, and more particularly to a method of controlling communications in such a node.
2. Description of the Background Art
In a telecommunications system, such as a sensor network or a local area network (LAN), formed by a plurality of communication nodes spatially disposed in an area or carried on mobile bodies, data or signals are transmitted between those nodes with collisions therebetween avoided which may be caused by electromagnetic interference, for example.
In order to avoid such collisions to accomplish successful data transmission, there have been presented a variety of collision avoiding or detecting systems, such as a TDMA (Time Division Multiple Access) system and a CSMA (Carrier Sense Multiple Access) system represented by a CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) and a CSMA/CD (Carrier Sense Multiple Access with Collision Detection) system, as generally taught by Y. Matsushita, et al “Wireless LAN Architecture” pp. 47, 53-59 and 69, Kyoritsu Shuppan Co., Ltd., Tokyo, Japan, 1996.
In the CSMA system, a node intending to transmit data determines another node transmitting data by the presence of a carrier frequency so as to transmit data during the absence of transmission by the other nodes. In the CSMA system, the heavier the traffic between the nodes, the more the overhead, thus the efficiency in data transmission being inavoidably reduced.
In the TDMA system, time slots are specifically assigned to nodes, each of which transmits data in a specific time slot thus assigned. A TDMA system where nodes are dynamically changeable in data transmission may be designed such that one node, called control, or management, node, controls the adaptive assignment of the time slots to the nodes.
The TDMA system has a drawback that the malfunction of a control node would cause the entire communications system to fall down. The dynamic reassignment of time slots to nodes is so complicated in processing as not to cause the system to be quickly adaptive to erratic surrounding conditions. In addition, the TDMA system is not so flexible that the duration of the time slots is unchangeable.